Considered most pertinent of the prior art are the U.S. patents issued to Rehm, U.S. Pat. No. 3,490,828, and Nothnagle, U.S. Pat. No. 3,650,597.
The Rehm patent discloses a microscope having an illumination system which includes a fixed mirror arranged in spaced relationship to a light source below the stage, and further including a mirror pivotally mounted on a carrier so that it may be oriented along the axis of the light source in order to reflect the light either to the fixed mirror or directly to the specimen being viewed by oblique side lighting. The Rehm system takes up valuable space at the front of the microscope for the rotatable mirror and requires delicate alignment of the fixed mirror.
The Nothnagle patent discloses a microscope having an illumination system which includes a mirror and a fixed light source. The mirror is carried by a mounting which may be shifted to one of two positions on a wall forming part of the microscope base. In one position the mirror reflects rays from the light source so as to be coincident with the optical axis of the objective for bright-field illumination of the subject being viewed. In the other position the mirror reflects rays from the light source so as to diverge from the optical axis of the objective leaving only such rays to enter it as may have been caused to reflect or scatter by details of the subject being viewed.
Since the mirror in the Nothnagle patent is movable to only two positions, its usefulness for dark-field illumination is limited. Further, movement of the mirror from one position to the other required manual disengagement of parts to permit such movement and reengagement of parts to hold the mirror in its shifted position, and great care had to be exercised to make sure the mirror was correctly seated in its adjusted position. Also, to change mirror position, the work had to be performed from beneath the microscope base.
My invention overcomes the above-noted problems of the prior art by providing construction whereby the mirror may be easily moved to any one of a number of positions to provide for bright-field illumination or varying degrees of dark-field illumination. The mirror is carried by a mounting that smoothly slides horizontally along the defining walls of a slot in a side wall of the microscope base. The mounting also permits the mirror to be rotated about a horizontal axis which is transverse to the sliding movement of mirror mounting.
A second mirror is carried by a mounting block in which the lens body is supported. The mounting block is movable vertically of the frame of the microscope by well-known focusing mechanism. The second mirror is pivotally mounted on the supporting block to catch rays emanating from a light source that is disposed within the microscope base to concentrate light at any selected position along the stage.
A single light source serves to beam rays to both mirrors and the first-named mirror may be moved horizontally to a position adjacent to the light source to block light rays and thereby make the microscope inoperable for both bright-field and dark-field illumination.